Trip device for circuit breaker



March 22, 1966 R, c, .NGWERSEN 3,242,289

TRIP DEVICE FOR CIRCUIT BREAKER Filed Aug. 26, 1963 2 Sheets-Sheet 1 ji i o 6 6 Z 67' M n f -,B/fl5 0 7 02 p 70 74 E- ---J E INVENTOR.

Zia/Z274 Z, fi zdcvis'efi awn 9 March 22, 1966 R. c. INGWERSEN TRIP DEVICE FOR CIRCUIT BREAKER 2 Sheets-Sheet I Filed Aug. 26, 1963 United States Patent Ofilice 3,242,289 Patented Mar. 22, 1966 3,242,289 TRIP DEVICE FOR CIRCUIT BREAKER Richard C. Iugwersen, Jackson, Mich., assignor to Mechanical Products Inc., Jackson, Mich., a corporation of Delaware Filed Aug. 26, 1963, Ser. No. 304,334 1 Claim. (Cl. 200-116) This invention relates generally to electric circuit breakers, and more particularly to an improved trip device for an electric circuit breaker.

Automatic electric circuit breakers generally comprise a pair of separable contacts, an operating mechanism that is releasable to effect separation of the contacts, and a trip device responsive to predetermined electrical conditions in an electrical circuit to effect release of the operating mechanism. Generally, the trip device comprises a latch mechanism and a current responsive element that effects movement of the latch mechanism to a release condition. Both of these components must satisfy certain basic requirements in order that the circuit breaker be positive in operation, durable, and consistent in performance.

The latch mechanism must have a relatively large latch surface to preclude spurious unlatching due to, for example, vibration, yet must unlatch the operating mechanism upon relatively slight movements of the current responsive member. The current responsive member must be sensitive to relatively slight current variations above a specific predetermined level and have a useable mechanical response characteristic.

It has long been a problem to produce a relatively inexpensive and compact trip device for a circuit breaker of relatively low current rating having both a significant mechanical response characteristic and aicurrent responsive element that is sensitive to relatively small overloads.

An improved trip device for a circuit breaker, in acc'ordance with the instant invention,,exhibits a relatively large mechanical movement due to relatively minute elongations of an electrically conductive wire having a positive temperature coefficient of-expansion. The wire is mechanically connected to a supporting arm in such a manner that elongation of the wire permits movement of a latching face on the arm in a direction substantially normal to'the longitudinal axis of the wire.

Accordingly, one object of the instant invention is an improved trip device for a circuit breaker.

Another object is a trip device having a large mechanical response due to relatively small overload currents.

Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a side 'elevational View of a single pole circuit breaker with one side of the housing therefor re moved;

FIG, 2 is a diagrammatic view showing deflection to the trip device;

FIG. 3 is a cross sectional view taken substantially along the line 33 of FIGURE 1; and

FIG. 4 is a fragmentary perspective view of the trip device of the instant invention.

As best seen in FIGURE 1 of the drawings, an electric circuit breaker comprises an insulating housing 12 molded from, for example, Bakelite. A .pair of terminals 14 and 16 extend from the housing 12 for connection to opposite sides of an external electric circuit.

The terminal 16 extends inwardly of the housing 12 for the support of a fixed contact20. A movable contact 22 is aligned and engageable with the fixed contact 20 to complete an electrical circuit through the circuit breaker 10 comprising the terminal 16, the fixed and movable contacts 20 and 22, a pigtail 24, a current responsive trip device generally designated by the numeral 26, a pigtail 28 and the opposite terminal 14.

The operating mechanism for the circuit breaker 10 is conventional in construction and, in brief, comprises a manual operator or plunger 29 that extends externally of and is slidably supported by the housing 12 for in and out movement. The manual operator 29 comprises an inner plunger portion 30 having an upper end 31 that extends into a guideway 32 formed in an upper wall 34 of the housing 12. A transversely extending pin 36 is fixedly supported by the housing 12 and extends through a slot 38 in the inner plunger portion 30 so as to guide the manual operator 29 for reciprocation.

A pair of pins 40 and 41 are supported on a lower end portion 42 of the inner plunger 30 and extend through slots, one of which is shown, and designated by the numeral 44, in an outer plunger portion 43 of the manual operator 29. The pins 40 and 41 and slots 44 function as a lost motion connection between the inner and outer plunger portions 30 and 4-6 of the manual operator 29.

The inner plunger 30 has a molded central hub portion 48 that is rigidly affixed thereto for the support of a rotatable contact carrier 70, as will be described.

The outer plunger portion 46 of the manual operator 29 extends through a ferrule 49 in a front wall 50 of the housing 12 and has a knob 52 secured thereto as by a pin 54. The knob 52 is preferably formed from an insulating material, for example, Bakelite, and is shaped to facilitate manual operation of the circuit breaker 10.

The outer plunger portion 46 of the manual operator 29 is normally urged outwardly of the housing 12 by a helical compression spring 56 that extends between a complementary spring retainer recess 58 in the knob 52 and a fixed abutment plate 60 fixedly supported by the housing 12.

The inner plunger portion 30 of the manual operator 29 is normally resiliently urged outwardly of the housing 12 by a tensioned coil spring 62 having one end portion 64 connected to a bracket 66 on a contact carrier 70. The other end portion 72 of the spring 62 is connected to a link member 74 that is pivotally connected to'a bell crank 7 6. The bell crank 76 is pivoted on a pin 78 journaled in ment outwardly of the housing 12 under the bias of the spring 56 and the inner plunger portion 30 from movement outwardly of the housing 12 under the bias of the spring 62.

However, when tension of the spring 62 is relieved upon automatic opening of the circuit breaker 10, as will be described, the spring 56 is sufficiently strong to bias the outer plunger portion 46 of the manual operator 29 downwardly, camming the roller 88 counterclockwise out of the notches 90 and 92, permitting continued outward movement of the outer plunger shaft 46 under the bias of its operating spring 56. Similarly, the inner plunger shaft 30 is released for downward movement under the reduced bias of the spring 62. Movement of the roller 88 outwardly of the notches 90 and 92 is also effected upon downward movement of the outer plunger portion 46, upon manual operation of the circuit breaker 10.

The contact carrier 70 is pivotally supported by a pin that extends through the hub 48 on the inner plunger portion 30 of the manual operator 29. The contact carrier 70 has a latching surface 102 thereon that underlies in coextensive relation with a complementary latching surface 104 on the trip device 26, to be described.

Upon disengagement of the latching surfaces 102 and 104 on the contact carrier 70 and trip device 26, respectively, the contact carrier 70 rotates counterclockwise to carry the movable contact 22 out of engagement with the fixed contact 20, thereby to break an electrical circuit through the circuit breaker 10.

In accordance with the instant invention, the trip device 26 comprises a resilient arm 108 of generally L- shaped configuration made from, for example, spring bronze. The arm 108 has a lower end portion 110 that is rigidly affixed to a generally U-shaped trip device support bracket 112, as by a pair of rivets 114 and 115. The support bracket 112 is fixedly secured to the housing 12 as by a pair of rivets 116 and 117.

The arm 108 of the trip device 26 has an upper end portion 118 folded generally normally to the lower end portion 110 thereof for the support of a generally square insulating block 120. The block 120 is retained on the upper end 118 of the arm 108 as by a pair of ears 122 and 124. It is to be noted that the block 120 has a downwardly extending tubular portion 126 that extends through a complementary aperture 130 in the end portion 118 of the arm 108 so as to insulate an upper end portion 132 of a current responsive wire 134 from the upper end 118 of the arm 108.

The current responsive wire 134 is made from, for example, Nichrome, and has a positive temperature coeflicient of expansion so as to elongate when heated.

As best seen in FIGS. 3 and 4, the upper end portion 132 of the wire 134 is secured, as by welding, to a conductive plate 136, superimposed on top of the insulating block 120. A pigtail 28 is also secured to the plate 136 to effect electrical connection with the terminal 14.

A lower end portion 138 of the wire 134 is secured to an outwardly extending car 140 on the U-shaped tn'p device support bracket 112, as by welding. The pigtail 24 is also electrically connected to the bracket 112. Thus, it will be seen that a conductive path is provided through the trip device 26 from the pigtail 24 through the wire 134, the plate136 and the pigtail 28. It is to be noted that upon assembly of the wire 134 and arm 108, the arm 108 is retracted from a normally deflected condition, shown in dashed lines in FIG. 2, to the condition shown in solid lines in FIG. 2 against the inherent resiliency of the arm 108.

As best seen in FIGURE 1 of the drawings, calibration of the trip device 26 is efi'ected by advancement or retrac; tion of a calibration screw 142 that is threadably received in a complementary aperture 144 in the bracket 112. A suitable aperture 146 is provided in the housing 12 of the circuit breaker to facilitate rotation of the screw 142.

As best seen in FIG. 2 of the drawings, elongation of the current responsive wire 134 permits clockwise rotation of the upper end portion 118 of the arm 108 relative to the bracket 112 of the trip device due to the inherent spring bias of the arm 108. Since the wire 134 extends generally parallel to the arm 108, movement of the arm 108 thereof under its inherent bias is generally normal to the longitudinal axis of the wire 134. Thus, a relatively small increment of elongation of the wire 134 permits a relatively large angular movement of the upper end portion 118 of the arm 108. In this manner, sensitivity of the trip device 26 due to relatively small current overloads is maximized, as is the permissible overlap between the latching surfaces 102 and 104 on the contact carrier and arm 108, respectively.

It is to be understood that the specific construction of the improved trip device for a circuit breaker herein disclosed and described is presented for the purpose of ex. planation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claim.

What is claimed is:

In an electric circuit breaker comprising a pair ofseparable contacts and an operating mechanism having a latch thereon releasable to effect separation of said contacts, an improved trip device sub-assembly for releasing said operating mechanism comprising an elongated relatively stiff inherently resilient member having a fixed end and an opposite end movable in a first direction relative to said fixed end, said movable end having a latching. surface thereon engageable with the latch on the operating mechanism of the circuit breaker, and a current responsive wire having a positive temperature coefficient of expansion, means on the fixed end of said resilient member directly connecting said wire thereto, means on the free end of said resilient member directly connecting said wire thereto whereby said trip device is insertable into andv removable from the circuit breaker as a sub-assembly, said wire extending between said means on the fixed and movable ends of said resilient member in spaced substantially parallel relation to said resilient member and normally pulling said member in a direction opposite to said first direction to said parallel condition against its inherent: resiliency, elongation of said wire permitting said resilient member to move in said first direction in response to its inherent resiliency to retract the latching surface thereon from engagement with the operating mechanism of the. circuit breaker.

References Cited by the Examiner UNITED STATES PATENTS 1,560,597 11/ 1925 Meierjohan 2001 16 2,434,728 1/ 1948 Van Sant 200116 2,943,172 6/ 1960 Ingwersen 2001 16 FOREIGN PATENTS 383,105 10/ 1923 Germany. 415,795 7/1925 Germany. 699,183 11/ 1953 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

